For over 113 years, the Marine Biological Laboratory has offered the Embryology Course, which has played an important role in the training of American developmental biologists. The course trains pre- and postdoctoral students for research careers in developmental biology in a unique physical and intellectual environment, not duplicated elsewhere in the nation. The Embryology Course consists of a series of formal lectures, informal seminars, extended discussions, and intensive laboratory research experience delivered over a six-week period in the summer. Course students are selected who are committed to teaching and research careers in the field of developmental biology, and are chosen from an international applicant pool. Traditionally, a number of the students from each year's class later move into positions of leadership in the international developmental biology research community. The teaching faculty members are senior scientists in the field, some of whom serve as instructors and lead research modules in the course, and others will give lectures and lead discussion on individual topics. The course consists of three modules, each of which is about two weeks long. Each module is staffed by an average of three to four resident instructors plus a comparable number of outside lecturers. The themes of the modules change from year to year as important developments in the field change. The course introduces students to a large number of terrestrial and marine embryos including C. elegans, Drosophila, ascidians, sea urchins, amphibians, zebrafish, chick, and mouse. Approaches include current molecular biological technologies, embryonic manipulation, microinjection and micromanipulation, microscopy and computer enhanced imaging technologies, and a number of immunochemical and in situ hybridization approaches. Students are challenged to formulate and test hypotheses in a well-equipped research environment and under the guidance of experienced research faculty and assistants. In support of the course, the Marine Biological Library provides a unique learning environment, laboratory and support facilities, an animal collection facility, and an excellent research library.